The present invention is related to electromagnetic shielding and more particularly to shielding electromagnetic interference (EMI) with an EMI gasket.
Electromagnetic inference (EMI) is related to the introduction of unacceptable amounts of electromagnetic energy into an environment by electrical devices and equipment. For example, a desk top or lap top computer chassis may comprise a large plurality of micro-electronic components that perform various tasks. Electromagnetic energy is radiated due to the electrical switching operations of the components. Accordingly, the radiated electromagnetic energy may significantly degrade the performance of other devices, if the radiated electromagnetic energy is permitted to be introduced into a common environment.
EMI is physically related to the transmission and reception of electromagnetic energy. Specifically, a source (alternatively referred to as an emitter herein) generates electromagnetic energy. The electromagnetic energy is radiated to a receiver (alternatively referred to as a receptor herein). The radiation of the electromagnetic energy to the receiver may cause the receiver to act in an undesired and often unpredictable manner.
EMI shielding is often utilized to reduce or eliminate the effects of EMI. Such shielding involves placement of an electromagnetic shield or EMI shield between an EMI source and potential EMI receivers. The electromagnetic shield may be a continuous metal sheet. The electromagnetic shield may adopt alternative forms such as a perforated metal sheet to permit thermal radiation. The electromagnetic energy emitted by a source propagates as an electromagnetic wave. The electromagnetic wave is partially absorbed by the EMI shield. Accordingly, the intensity of the electromagnetic wave is attenuated or reduced and the EMI effects upon receivers are lessened.
The design of the electromagnetic shield significantly impacts its effectiveness in reducing the intensity of the electromagnetic wave associated with the EMI. Specifically, a gap or seam in an electromagnetic shield will cause EMI leakage. Accordingly, EMI gaskets are utilized to prevent gaps or seams from causing EMI leakage. EMI gaskets are conductive media designed to provide a flexible connection between two electrical conductors that are being used as EMI shields. EMI gaskets are selectively placed to reduce any slots, seams, or other discontinuities between the EMI shields to prevent EMI leakage.
An important characteristic of EMI gaskets is their ability to facilitate acceptable electrical contact between the two conductors. Typically, EMI gaskets are compressed to provide a sufficient contact force between the EMI gaskets and the respective conductive surfaces. The contact force increases the electrical contact between the two conductors via the EMI gasket. However, typical devices that utilize an external or closure force to facilitate the electrical contact have several disadvantages. First, application of an external force to typical EMI gaskets is problematic because the tolerance associated with this approach is quite small. Deviation from the appropriate compression force may either allow EMI leakage or damage the EMI gasket.
Additionally, EMI gaskets typically provide a spring force for positioning purposes. As depicted in FIG. 1, known system 100 includes EMI gasket 103 that utilizes a spring force. When points A and B of EMI gasket 103 are displaced from their equilibrium position, a spring force is encountered due to the structural rigidity of EMI gasket 103. EMI gasket 103 is placed on conductive medium 102 that is typically a part of a chassis of system 100. EMI gasket 103 is opened during placement on conductive medium 102, i.e., the distance between points A and B is increased. A spring force is encountered that impinges EMI gasket 103 on conductive medium 102 at points A and B. Accordingly, the spring force tends to keep EMI gasket 103 from being displaced.
EMI gasket 103 is compressed between conductive medium 101 (e.g., a chassis cover) and conductive medium 102. This increases the contact forces associated with points A and C of gasket 103. However, the compression deforms EMI gasket 103. The deformation causes a deformation force at point B. The deformation force opposes the spring force thereby reducing the effectiveness of the spring force to hold EMI gasket 103 in its desired position.
Other various mechanisms may be utilized to lock the EMI gaskets in place to facilitate the electrical contact. For example, corresponding holes, flanges, and locking bolts may be utilized to lock EMI gaskets in a desired position. However, locking EMI gaskets in this manner requires some amount of manual configuration upon assembly. Additionally, removal of the EMI gaskets to access shielded electronic components requires additional manual manipulation.
In one embodiment, the present invention is directed to a system for shielding electromagnetic energy. The system comprises an electromagnetic interference (EMI) gasket comprising at least one longitudinal member that is operable to exert a spring force upon deflection and at least one lance member; and a chassis comprising a lip member, the lip member being operable to accept the EMI gasket, a base member that is operable to deflect the at least one longitudinal member when the EMI gasket is placed over the lip member, and a locking member that is adapted to latch the at least one lance member in a latched position when the EMI gasket is placed over the lip member, wherein the spring force is operable to retain the at least one lance member in the latched position and the spring force is operable to facilitate electrical contact between the base member and the EMI gasket.